Field of the Invention
The present invention relates to the field of measuring the geometry of fiber optic ferrules used in multi-fiber connectors by means of interferometric microscopes. More specifically, the invention relates to guide holes parallelism and fiber angle interferometric measurement, as well as the location of the fiber holes on the ferrule end face.
Description of the Related Art
Manufacturers of fiber optic connectors seek ways to produce the connectors with low transmission loss and low back reflection. End faces of fiber optic connectors must satisfy certain criteria for effective fiber mating as required by the industry standards. They must be clean and their surface geometry must provide for good physical contact and low signal loss.
Various methods are applied for inspecting connector end faces by means of interferometric microscopes (see U.S. Pat. No. 5,459,564 A and U.S. Pat. No. 6,705,767 B1). In the above cited inventions, connectors are so aligned in the interferometric system that their end faces are perpendicular to the optical axis of the interferometric microscope. Such analysis methods aim at inspecting connector end faces from which interferometry data is obtained.
In addition to the end face inspection of fiber optic connectors for the purpose of measuring parameters of the end face surface, there is a need in measuring other connector and ferrule parameters. For example, it is necessary to measure parallelism and position of guide pin holes and fiber holes of multi-fiber ferrules.
In multi-fiber connector plugs two guide pins enable precise alignment between mating male and female connectors to minimize the optical insertion loss. When the two guide pins of a male connector are inserted into the guide holes of a female connector, the connectors are mated properly and good physical contact is achieved.
For the precise fiber alignment of multi-fiber connectors, it is also important that the axes of the fibers are not tilted relative to each other and relative to the axes of the guide pin holes. Ideally, the axes of the fiber holes must be parallel to each other and to the axes of the guide pin holes.
In addition to parallel alignment of the guide pin holes and the fiber holes, it is also important that the multiple optical fiber holes are not deviated from their designated locations on the end face along the axis that passed through the guide hole centers as set in the industry standards.
Manufacturers of fiber optic connectors need to measure the parallelism and position of the guide holes and fiber holes to insure the quality of their connectors and the compliance with the industry standards. It has not been possible to measure these parameters by end face scanning.
There are known methods for measuring XY fiber hole deviations from designated locations. The method suggested by International Electrotechnical Commission standard IEC 61300-3-27 describes the measurement procedure by means of a 2D microscope accompanied with other equipment. The method declared in U.S. Pat. No. 8,699,012 B2 describes how to measure fiber alignment by detecting XY positions of light beams that pass through guide pin holes and fiber holes. Both methods allow to determine XY positions of fiber holes and guide holes.
The present invention suggests inserting reference fibers into the fiber holes and reference guide pins into the guide pin holes and then scanning these inserted fibers and guide pins from side by an interferometric microscope. The reference fibers and guide pins also represent 3D positions and angles of the fiber holes and the guide holes. Subsequently, it is possible to determine locations of guide pin holes and fiber hole on ferrule end face.